1. Field of the Invention
The present invention generally relates to optical disk recording apparatuses and methods of recording data on optical disks, and more particularly to an optical disk recording apparatus that records data on an erasable optical disk and a method of recording data on an erasable optical disk.
2. Description of the Related Art
Direct-read-after-write optical disks are of two general types: write-once and erasable. In overwriting an erasable optical disk, a laser beam having a laser power alternating between a write power Pw and an erase power Pe is employed. In this case, the write power Pw forms pits on the recording film of the optical disk by changing the state of the recording film from a crystalline state to an amorphous state, and the erase power Pe erases the pits by changing the state of the recording film from the amorphous state to the crystalline state.
The Optimum levels of the write and erase powers Pw and Pe (optimum write and erase powers Pwo and Peo) of the laser beam at a time of recording data on an optical disk differ depending on a type of the optical disk, a recording apparatus, and a recording rate. Therefore, in order to set the optimum write and erase powers Pwo and Peo based on the combination of a type of the optical disk, a recording apparatus, and a recording rate employed in a practical recording, a recording power calibration called OPC (Optimum Power Control) is performed prior to the recording of data.
A description will be given of an OPC operation in a conventional optical disk recording apparatus for an erasable optical disk.
FIG. 1 is a diagram for illustrating the test recording area of the optical disk.
As shown in FIG. 1, a data area for storing a variety of data and a PCA (Power Calibration Area) that is a test recording area for setting the optimum write power of a laser beam are formed on the recording surface of the optical disk. The PCA, which is formed along a track closest to a disk center, includes a test area and a count area. The test area is formed of 100 partitions, and each partition is formed of 15 frames. In one OPC operation, one partition is used so that each frame of the partition is recorded with a test signal with a different level of the laser power. That is, the laser power has the 15 levels. Each test signal is an EFM-modulated signal formed of a pulse train having a pulse width three to ten times a reference pulse width T, and is recorded on each frame with pits of nine types of lengths. The reference pulse width T is for one cycle of a pulse signal having a frequency of 4.32 MHz, and is 230 nsec at a normal rate (1xc3x97).
The laser beam is emitted onto each frame so that each test signal is reproduced by detecting a light reflected back therefrom. At the same time, a modulation degree m as an index indicating the magnitude of the amplitude of each reproduced HF (high frequency) signal is measured by using the following equation
m=I11/Itopxe2x80x83xe2x80x83(1) 
where I11 is an amplitude of a reproduced HF signal based on pits and lands (regions between pits) of a pulse width 11 times the reference pulse width T, and Itop is the optical reflectivity of the lands as shown in FIG. 2. In FIG. 2, I3 is an amplitude of the reproduced HF signal based on pits and lands of a pulse width three times the reference pulse width T. The modulation degree m differs depending on the level of the write power Pw.
As shown in FIG. 3, as the level of the write power Pw becomes lowers, the modulation degree m becomes smaller because the amplitude of the reproduced HF signal becomes smaller. On the other hand, as the level of the write power Pw becomes higher, the modulation degree m becomes larger because the amplitude of the reproduced HF signal becomes larger. If the write power Pw is increased to a certain level, the modulation degree m becomes saturated. The write power Pw of the level at which the modulation degree m starts to be saturated minimizes a jitter or error in recording data. Therefore, the write power Pw of that level is determined to be the optimum write power Pwo.
In the case of determining the optimum write power Pwo by the modulation degree m, a method using a parameter xcex3 obtained from the characteristic of the modulation degree m is employed. The parameter xcex3 is given by the following equation
xcex3=(dm/dPw)xc3x97(Pw/m)xe2x80x83xe2x80x83(2) 
That is, the parameter xcex3 is the differential of the characteristic of the modulation degree m. The optical disk is prerecorded with the target value xcex3 target of the parameter xcex3 as ATIF (Absolute Time In Pregroove) information. Therefore, as show in FIG. 4, the characteristic of the parameter xcex3 is obtained from the characteristic of the modulation degree m according to the above-described equation (2), and then a write power level Ptarget that realizes the target value xcex3 target is obtained. Since the optical disk is prerecorded with a coefficient xcfx81 for obtaining the optimum write power Pwo from the write power level Ptarget as the ATIP information, the optimum write power Pwo is obtained, by using the coefficient xcfx81, from the following equation
Pwo=xcfx81xc3x97Ptargetxe2x80x83xe2x80x83(3) 
The optimum write power Pwo obtained from the above-described equation (3) is set and used as a write power at the time of a signal recording. The optimum erase power Peo is set, by using the optimum write power Pwo, and coefficients xcex5 and xcexa recorded on the optical disk as the ATIP information, based on the following equations
Peo=xcex5xc3x97Pwoxe2x80x83xe2x80x83(4) 
Peo=xcex8xc3x97xcex5xc3x97Pwoxe2x80x83xe2x80x83(5) 
Here, the coefficient xcex5 is a Pe/Pw ratio, and the coefficient xcexa is a Pe/Pw ratio compensation coefficient for a low-speed recording.
The optimum write and erase powers Pwo and Peo of the laser beam provided by the OPC operation in the unrecorded test recording area are also employed in overwriting data onto a recording area of the erasable optical disk which area is already recorded with a signal so that pits are formed in the recording area. However, the signal recorded on the recording area by the write power Pw of a high level cannot be erased completely unless being erased by the erase power Pe of a level as high as a certain level.
However, if the write and erase powers Pw and Pe for overwriting are set to higher levels to improve recording characteristics such as a jitter and a block error rate at a time of overwriting (overwriting recording characteristics), deeper pits are formed so that the durability of the optical disk is impaired.
It is a general object of the present invention to provide an optical disk recording apparatus and a method of recording data on an optical disk in which the above-described disadvantages are eliminated.
A more specific object of the present invention is to provide an optical disk recording apparatus and a method of recording data on an optical disk which apparatus and method improve recording characteristics at the time of an overwriting and the durability of an optical disk.
The above-objects of the present invention are achieved by a recording apparatus for an erasable optical disk, which apparatus includes: a first part which measures a modulation degree of a signal reproduced from an area of the optical disk at a time of overwriting first data recorded in the area with second data; a second part which determines a first write power level corresponding to the modulation degree measured by the first part based on a relation between write power levels and modulation degrees of signals reproduced from a test recording area of the optical disk, the signals being recorded therein with the corresponding write power levels different from one another; a third part which obtains a target modulation degree corresponding to a type of and a recording rate for the optical disk from one of tables prestoring modulation degrees corresponding to optical disk types and recording rates; and a fourth part which obtains a write power level for overwriting from the first write power level based on a comparison between the target modulation degree and the modulation degree measured by the first part, wherein the recording apparatus overwrites the first data with the second data with the write power level for overwriting.
The above-objects of the present invention are also achieved by a recording apparatus for an erasable optical disk, which apparatus includes: a first part which measures a modulation degree of a signal reproduced from an area of the optical disk at a time of overwriting first data recorded in the area with second data; a second part which determines a first write power level corresponding to the modulation degree measured by the first part based on a first relation between write power levels and modulation degrees of signals reproduced from a test recording area of the optical disk, the signals being recorded therein with the corresponding write power levels different from one another; a third part which obtains, based on the first relation, a second relation between the write power levels and modulation parameters obtained from the modulation degrees; a fourth part which obtains, based on the first and second relations, a target modulation degree corresponding to a target modulation degree parameter read from the optical disk; and a fifth part which obtains a write power level for overwriting from the first write power level based on a comparison between the target modulation degree and the modulation degree measured by the first part, wherein the recording apparatus overwrites the first data with the second data with the write power level for overwriting.
The above-objects of the present invention are also achieved by a recording apparatus for an erasable optical disk, which apparatus includes: a first part which measures a modulation degree of a signal reproduced from an area of the optical disk at a time of overwriting first data recorded in the area with second data; a second part which determines a first write power level corresponding to the modulation degree measured by the first part based on a relation between write power levels and modulation degrees of signals reproduced from a test recording area of the optical disk, the signals being recorded therein with the corresponding write power levels different from one another; a third part which obtains a target modulation degree from the relation between the write power levels and the modulation degrees; and a fourth part which obtains a write power level for overwriting from the first write power level based on a comparison between the target modulation degree and the modulation degree measured by the first part, wherein the recording apparatus overwrites the first data with the second data with the write power level for overwriting.
The above-objects of the present invention are also achieved by a method of recording data on an erasable optical disk, which method includes the steps of (a) measuring a modulation degree of a signal reproduced from an area of the optical disk at a time of overwriting first data recorded in the area with second data; (b) determining a first write power level corresponding to the modulation degree measured by the step (a) based on a relation between write power levels and modulation degrees of signals reproduced from a test recording area of the optical disk, the signals being recorded therein with the corresponding write power levels different from one another, (c) obtaining a target modulation degree corresponding to a type of and a recording rate for the optical disk from one of tables prestoring modulation degrees corresponding to optical disk types and recording rates, (d) obtaining a write power level for overwriting from the first write power level based on a comparison between the target modulation degree and the modulation degree measured by the step (a), and (e) overwriting the first data with the second data with the write power level for overwriting.
The above-objects of the present invention are also achieved by a method of recording data on an erasable optical disk, which method includes the steps of, (a) measuring a modulation degree of a signal reproduced from an area of the optical disk at a time of overwriting first data recorded in the area with second data, (b) determining a first write power level corresponding to the modulation degree measured by the step (a) based on a first relation between write power levels and modulation degrees of signals reproduced from a test recording area of the optical disk, the signals being recorded therein with the corresponding write power levels different from one another, (c) obtaining, based on the first relation, a second relation between the write power levels and modulation parameters obtained from the modulation degrees, (d) obtaining, based on the first and second relations, a target modulation degree corresponding to a target modulation degree parameter read from the optical disk, (e) obtaining a write power level for overwriting from the first write power level based on a comparison between the target modulation degree and the modulation degree measured by the step (a), and (f) overwriting the first data with the second data with the write power level for overwriting.
The above-objects of the present invention are further achieved by a method of recording data on an erasable optical disk, which method includes the steps of (a) measuring a modulation degree of a signal reproduced from an area of the optical disk at a time of overwriting first data recorded in the area with second data, (b) determining a first write power level corresponding to the modulation degree measured by the step (a) based on a relation between write power levels and modulation degrees of signals reproduced from a test recording area of the optical disk, the signals being recorded therein with the corresponding write power levels different from one another, (c) obtaining a target modulation degree from the relation between the write power levels and the modulation degrees, (d) obtaining a write power level for overwriting from the first write power level based on a comparison between the target modulation degree and the modulation degree measured by the step (a), and (e) overwriting the first data with the second data with the write power level for overwriting.
The above-described apparatuses and methods take into consideration the fact that the overwriting recording characteristics depend greatly on the states, or depths, of pits already formed on the optical disk, that is, the modulation degree. Therefore, according to the above-described apparatuses and methods, the overwriting recording characteristics as well as the durability of the optical disk are improved.